A known intake manifold for an internal combustion engine, defining an intake passage, disclosed in, for example, Patent Document 1 is formed by joining together two or more structural parts. One of the structural parts is integrally provided with an inlet connecting part to be joined to a throttle device, an outlet flange to be joined to the cylinder head of the internal combustion engine, and a connecting part connecting the inlet connecting part and the outlet flange. The joining parts of the structural parts are joined together to build the intake manifold.    Patent Document 1: JP 2004-308506 A